# Does the light transform a matter?

1. Aug 21, 2004

### canopus

I've been dwelling on this question for hours! Does the light transform a matter? It seems it does..... A high energetic photon transform an electron and a positron. Hmm, how can it transform then?

PS:I guess this subject is much suitable for physics.

2. Aug 21, 2004

### mlip

Light is energy and matter is energy... so maybe. Sorry I'm no more help :)

3. Aug 22, 2004

### ArmoSkater87

Mass and energy are interchangeable, since light is energy, it can be converted into matter. A very high energetic photon of light (xray, gamma ray) can transform into an electron and positron pair. Light transforming into matter is the opposite of the positron and electron anihhilating each other and being converted into two gamma rays, released in opposite directions.

4. Aug 22, 2004

### ArmoSkater87

5. Aug 22, 2004

### canopus

Thanks for the detailed information. It really helped me!

6. Aug 22, 2004

### pmb_phy

It is incorrect to say that light is energy. It is correct to say that light has energy.

Pete

7. Aug 22, 2004

### Vern

This seems to suggest that light is a thing that has the property, energy. But if you remove all the energy from light, what is left?

Keep on chuggin !!

Vern

8. Aug 22, 2004

### canopus

Nothing is left (;

9. Aug 22, 2004

### Prometheus

Who, specifically, is this "you" that you are talking to? If it isn't some omnipotent god, then forget it, because the suggestion of removing all energy from light is not very meaningful.

10. Aug 22, 2004

Light has 0 rest mass, so it is not energy, you have no mass or energy left.

11. Aug 22, 2004

### ArmoSkater87

When antimatter and matter annihilate, they are converted into ENERGY...not something that HAS energy. It so happens that this energy is gamma rays. Therefore light IS energy. If light was something that HAD energy, then if it gave away all of its energy to some substance, there would be a stationary photon left...with no energy, and we all know that this cant be, and isnt true at all.

12. Aug 23, 2004

### pmb_phy

That's like saying that a car as the property of speed. Speed is not an inherent property of a car.
No energy, no photon. That can never be taken to mean that a photon and energy are the same exact thing. There is a one-to-one relationship. That is all. There is a one-to-one relationship between the volume of a sphere and the radius of a sphere. No radius - no sphere. But it is incorrect to say that radius and volume are different names for the same thing.
That is incorrect. See above.
That is incorrect. A photon can give up some of its energy, e.g. by scattering off of an electron. An photon can give up all of its energy by being absorbed by an atom. When it does so the photon no longer exists, it doesn't mean that its at rest.

Pete

13. Aug 23, 2004

what do you mean. When a matter and its anti matter particle anniahlate, they form pure energy.

14. Aug 23, 2004

### daveed

one question.
light has 0 rest mass, yes? but light is never at rest... so couldn't you take the mass then as the momentum/c?
but then again, this whole business is quite tricky

15. Aug 23, 2004

### Tom Mattson

Staff Emeritus
No, they form photons. Photons are not "pure energy", they are...well...photons!

PMB had it just right above: Photons are not energy, they have energy.

Photons have spin and parity too, but we don't say that they are "pure spin" or "pure parity". They have those properties, they are not identical to them.

16. Aug 23, 2004

### pmb_phy

I forgot to mention that pair production from a single photon can't occur in a vaccum. It must occur near the nucleus of an atom. The nucleus sort of acts like a catalyst in that way. If pair production from a single photon occured in a vaccum then momentum wouldn't be conserved. The nucleas takes up some of that momentum.

Pete

17. Aug 23, 2004

who told you that anniahlation of an atimatter and matter particle produces photons?

18. Aug 23, 2004

### Tom Mattson

Staff Emeritus
QFT and experimental evidence say so. In fact, there's nothing else that a pair can produce when they annihilate, because it would violate known conservation laws.

19. Aug 24, 2004

### ArmoSkater87

No, that would give you the maximum mass into which that photon of light can be transformed into.

20. Aug 24, 2004

### pmb_phy

Yes. In fact (relativistic) mass is defined as the m in p = mv. So when v = c -> p = mc or m = p/c.

Pete